GASCO Calibration Gas 650es-416-CO2-4 200 PPM Carbon Monoxide, 20 PPM Hydrogen Sulfide, 2.5 % Methane (50 % LEL), 4 % Carbon Dioxide, 18 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA